1. Field of the Invention
This invention relates generally to dental implants. More particularly, this invention relates to endosseous dental implants having external or internal locking means for engaging an artificial dental appliance a dental restoration or prosthesis.
2. Description of Prior Art
There are basically three different types of endosseous implants blades, screws, and cylinders. Blade, screw and cylinder implants all require that a hole or slot first be made in the maxillary or mandibular jawbone prior to the implant being inserted In the case of a screw-type implant, a threaded hole is either tapped in the bone to accept the threaded screw implant, or alternatively a self-tapping threaded implant is screwed directly into the prepared bone. The tops of both these screw-type implants are typically provided with either a hexagonal male projection or an internal female hexagonal arrangement which is adapted to mate with a correspondingly shaped engaging male or female mating surface in a screw driving tool which is used to actually insert the implant into the bone. Following insertion of the screw type implant, the male projection or the female aperture of the implant can be utilized to matingly engage a corresponding female aperture or male projection in a prosthetic component to firmly seat the component and prevent rotation of the prosthetic component with respect to the implant. In this way, the prosthetic component is secured into position with the above screw type implant. A representative example of a screw-type implant is disclosed in U.S. Pat. No. 4,713,004 to Linkow et. al. which discloses an implant having inner and outer screw threads along its elongate body portion and a hexagonal projection at its upper end which is adapted to be engaged for rotation with a wrench type tool.
The prior art cylinder-type implants differ from the screw-type implants in several respects. First, the cylinder-type implants do not have external threads. Second, the cylinder-type implants typically have an open internal threaded central bore extending partially into the implant for the purpose of securing a prosthetic component. Third, the cylinder-type implants are not provided with hexagonal members extending from the tops thereof, because a threading tool is not necessary to install the cylinder-type implant as with a screw implant. In implanting a cylinder-type implant, an unthreaded hole is drilled into the bone, with the inner diameter of the hole being equal to or slightly less than the outer diameter of the cylinder to be installed. The cylinder is then carried to the surgical site by utilizing a carrying post which is threaded into the internal threaded central bore and which projects therefrom. The cylinder implant, with the carrying post extending therefrom, is then press fit into the hole and is gently tapped into place by tapping the carrying post with a small mallet (thereby protecting the implant itself). In the ideal case, a snug, tight fit is provided between the cylinder and the surgical osteotomy hole
The choice of whether to use a screw-type or a cylinder-type implant is strictly up to the dental surgeon and has previously been substantially dependent upon the quality, quantity, and geometry of bone underlying the gingiva at the implant site. The cylinder-type implant is often preferred where the bone of the mandible or maxilla is soft or less dense. Since the bone of the maxilla is typically softer than bone matter of the mandible, cylinders are often the implants of choice when used in the maxilla.
As aforementioned, the cylinder implant is installed by pushing the body portion thereof directly into the surgical site drilled into the bone. The top of the cylinder implant is located at approximately the surface of the bone and includes an internal threaded bore extending, into the cylinder body as noted above. This internal threaded bore receives anchoring fasteners such as screws to hold a prosthetic component or restoration in place above the cylinder implant
An abutment, which can take many forms and shapes is then placed on top of the cylinder or screw type implant. The abutment serves as a core to provide for retention and/or stability of a replacement tooth or dental prosthesis. The abutment is typically colineal with the central internal threaded bore of the cylinder when the abutment is in place on top of the cylinder. The replacement tooth or prosthesis typically also has an aperture colineal with the bore of the cylinder and the abutment. In such situations, a screw extending through the prosthetic device and the abutment is used to secure the abutment and the prosthetic device to the implant. In other cases, the prosthetic restorations are cemented onto the abutment core.
Heretofore, where the bone closest the gum of the patient is soft, the surgeon utilizing the cylinder-type implant has not had the benefit of any screw-implant engagement with the bone of the patient. Moreover, prior to the teachings of the parent application hereto, the surgeon has not had the advantage of a shaped projection member, mating with a corresponding aperture in the abutment in order to obtain a secure and relatively permanent fit and orientation between the cylinder and the dental replacement structure.